The early history of chondrite parent bodies inferred from 40Ar-39Ar ages.
Abstract
Ar-40-Ar-39 age determinations have been carried out on 16 relatively unshocked chondrites in order to investigate their early cooling history and by inference that of their parent bodies. Five of the samples showed evidence of having lost some argon relatively recently, but it was possible to deduce cooling ages for all but one of these based on high temperature age plateaux. The ages fall in a restricted interval from 4.52 to 4.42 Ga when calculated using the recently recommended decay constants. The age of most samples is indistinguishable from the mean age of 4.48 + or - 0.03 Ga. The narrow range of ages is consistent with the chondrites having initially cooled in parent bodies with radii less than 130 km or at shallower depths in larger bodies. While these results are in broad agreement with cooling rates based on Ni profiles in the metal phase and on Pu-244 fission track studies, they appear to be inconsistent with some of the very slow metal cooling rates (1 deg C/Ma) which have been reported.
- Publication:
-
Lunar and Planetary Science Conference Proceedings
- Pub Date:
- 1978
- Bibcode:
- 1978LPSC....9..989T
- Keywords:
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- Argon Isotopes;
- Chondrites;
- Meteorites;
- Radioactive Age Determination;
- Cooling;
- Rates (Per Time);
- Statistical Analysis;
- Tables (Data);
- HISTORY;
- ARGON-ARGON;
- AGES;
- COOLING RATES;
- PLANETESIMALS;
- CHONDRITES;
- THERMAL HISTORY;
- Lunar and Planetary Exploration; Meteorites;
- Chondrites:Thermal History